Intel fortran-80 manual Fen:• • • •

CHAPTER 2

FORTRAN CONCEPTS

The chapter discusses the concepts and terminology used to describe the structure and elements of a FORTRAN program.

2.1FORTRAN Program Structure

2.1.1Program Units and Procedures

The scope of many FORTRAN operations is defined to be a program unit. A pro- gram unit is either a main program or a subprogram.

A main program can start with a PROGRAM statement, though it need not. Sub- programs start with either a FUNCTION, SUBROUTINE, or BLOCK DATA state- ment. A FORTRAN program must have one and only one main program and may have any number of subprograms (Figure 2-1).

Subroutines and functions are called procedures. Subroutines and 'external' func- tions are further defined to be external procedures. External procedures can be created outside a FORTRAN program also; for example, a FORTRAN program can call an external procedure written in PL/M-80and stored in an ISIS-II system library. Procedures are discussed in detail in Chapter 5.

MAIN

PROGRAM

[PROGRAM]

•

•

•

•

END

SUBPROGRAMS

SUBROUTINEJ

•P-'S~UB=R=OU=T=IN=E

FEN:• • • •

									END
			FUNCTION						J
				•
									FUNCTION
				•
..		..		•		•	•	•
			END						,...
	1 -								END
			BLOCK DATA						J
				•
									BLOCK DATA
				•				•
		~		•		•	•
			END
									END
			f'-
					~
			'-----"
			MISC.
			EXTERNAL
			PRO-
			CEDURES

~

Fig. 2-1Program Units

2-1